Field of Invention
The present invention relates to semiconductor devices. More particularly, the present invention relates to a semiconductor structure of a control gate.
Description of Related Art
In the family of nonvolatile memory devices, flash memory is an improved version of electrically erasable, programmable read-only memory (EEPROM). a split-gate nonvolatile memory (NVM) cell is provided typically is including two separating channel regions, controlled respectively by the floating gate and the control gate. Data is stored by modulating the threshold voltage (Vt) of the field effect transistor (FET) through hot carriers injection (HCl) through a dielectric layer into the charge storage element.
A split-gate thin film storage memory cell is a split-gate NVM cell having discontinuous charge storage elements like nanocrystal dots in a dielectric layer. The split-gate thin film storage memory cell has many benefits like simple operation, fast read access, lower power to read/write, and have simple fabrication process than the split-gate NVM cell. In order to continuously scale down the cell size, the split-gate thin film storage flash memory is proposed for embedded flash device. But the traditional charge storage elements formed by low pressure chemical vapor deposition (LPCVD) have their density limitation. When the split-gate NVM cell keeps scaling down, the effect of the charge storage elements density becomes significant. The density of the charge storage elements has directly connection with the threshold voltage, and low charge storage element density also brings poor program efficiency.